Telephone system



Jan. 29, 1929. 1,700,320

' C. J. LARSEN TELEPHONE SYSTEM Filed Aug. 28, .1926

Patented Jan. 29, 1929.

MTED STATES 1,700,320 PATENT orrics.

CHRISTIAN J. LARSEN, OF CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO AMERICAN ELECTRIC COMPANY, INC., OF CHICAGO, ILLINOIS, A CORPORATION OF MAINE.

TELEPHONE SYSTEM.

Application filed August 28, 1926. Serial No. 132,063.

The present invention, broadly stated, relates to telephone systems.

More particularly, the invention is concerned with a novel universal cord circuit for use in private branch exchanges which maintain inter-communication with main exchanges, over trunk lines, terminating in jacks at attendant operators switch boards in the private branch exchanges.

The principal aim of the invention is to.

provide a cord circuit for a private branch exchange, having universal wiring, in order to meet requirements for either manual or automatic exchange service.

In accordance with the above, one object of the invention is to provide means for-obtaining either through supervision or nonthrough supervision depending upon local requirements of the private branch exchange.

The cord circuit may be used as an ordinary manual link for interconnecting a calling with a called branch exchange subscribers line; or it may be used for c0nnecting a calling branch exchange station to a subscribers line in a manual or in an automatic main exchange, the attendant at the branch exchange serving in the latter case as medium for dialling the called partys telephone numher; and it may also serve for extending i11 coming calls from the trunk lines to stations in the branch exchange. IThe cord circuit is normally adapted to these classes of service. However, in accordance with the aim of the invention there are circuit changing means provided for adapting the cord circuit to be used for calls from a branch exchange station over a trunk line to a manual or to an automatic main exchange station, the setting of the switches in the latter case being under control of the branch exchange station subscriber operating his dial; other means, cooperating with the first, adapt the cord for so called through or night-set-ups, by which. is meant a connection between a certain branch exchange station and the trunk line, with the cord circuit as link, permitting the branch station to call main exchange parties, and vice versa, main exchange stations to reach the branch exchange party; and the cord may also be employed for toll calls.

It is another object of the invention to providea supervisory signal to the private branch exchange attendant under all classes of service.

provision in the cord.

A further object resides in means to operate the switches in an automatic main exchange, under control of a branch exchange station, as they are operated in case of a standard non-branch exchange station. More specifically, the action on the part of a branch subscriber who has called a main station, of restoring the receiver to thesWitch-hook at the termination of a call, causes instantaneous release of the main exchange apparatus, as is standard practice in such exchanges.

Another object is to be found in a re-call If the branch ex changeattendant delays taking down a connection between a branch to main exchange, or main exchange to branchconnection, and if the trunk is again selected before the connection is taken down, the attendant receives a supervisory signal. During the ringing period on the trunk, the calling supervisory lamp will be either flashed or steadily lighted, depending on the method employed for ringing. 1 e

In connection with the re-call provision intimated. in the preceding paragraph, there are means in the cord, to prevent the rering signal from ringing the bells on the branch station still connected, if the connection for which the trunk was used last had been one in which the operator had done the dialling.

W hen the branch station party hangs up the receiver, the station end of the cord is disconnected; therefore, only the attendant reccives the signal. If on the other hand, the cord has been set for through service, the trunk re-call signal would operate the branch exchange station bells, because, under this condition, the cord circuit is not opened by the act of the branch subscriber restoring the receiver to the switch-hook. This, of course, is desirable, since it is intended in throughservice, to signal the branch station connected to a trunk line. Y

A feature, somewhat related to the recall provision discussed above, resides in means to prevent ringing currentfrom entering the attendant operatorls telephone circuit prior to the tripping of the machine ringing. When the operator observes the ringing signal, she actuates her listening key to connect her telephone set to the cord. The operation of the relay, having the function of connecting the attendants telephone to the cord, is made dependent on the normal condition of the re-ring relay. Therefore, the connection of the operators circuit to the cord, is only possible during a silent period.

Another object is to furnish provisions for supplying battery to the waiting branch exchange subscriber while the attendant is dialling a wanted number. This prevents clicks in the receiver of the waiting party, and also provides convenient means for signalling the operator in case the waiting subscriber abandons the call during the dialling period.

Still another object is concerned with the prevention of disturbing clicks in the attendant operators receiver, while she is dialling. This is accomplished by a relay which is kept energized during dialling and short circuits the receiver of the operators set.

The above, and other objects and features of the invention will be brought outin the detailed explanation of the functions of the cord circuit which is yet to follow. Before entering a detailed discussion, a brief account of the drawing and the symbols used will be given, to aid understanding.

Referring now to the drawing, there is shown at the upper, lefthand side, a jack J. This jack represents a branch exchange subscribers line A, comprising the line conductors R and T. The line relay 1 is connected in bridge of the line conductors, and is adapted to operate the line signal lamp L. [it the upper, right-hand side of the drawing is shown an equipment, which is in all respects identical to the one at the left side, and serves a branch exchange subscribers line B. The lines are so call-ed non-multiple lines, which signifies that each line has only one jack terminating at an operators position. The substation apparatus of the lines A and B are not shown in order to keep the drawing as simple as possible, eliminating everything well known and not necessary for comprehending the invention.

At the lower, right-hand side of the drawing is shown a jack J A trunk line C, leading to a main exchange, and comprising the line conductors R and T terminates in this jack in the branch exchange. Relay 5 is connected in bridge of the talking conductors of this trunk line, in series with a condenser 7 for the purpose of operating a signal lamp L when the main exchange desires to call the operator in the branch exchange.

In the middle part of the drawing is shown the novel cord circuit, ending in the answering plug P and in the calling plug Pi RK and BK are the ringing keys; NT is the through-dial, toll-, and nigl'it-service key; LD is the dialand listening-key for the attendant operator; 16 and 39 are the answering and the calling supervisory lamps, re spectively; and the ringing current generators used in connection with this cord, are shown at Gr and G.

The reference character 0 indicates the attendant operators telephone set, comprising the traninitter 11, the receiver 13, the induction coil 1-2, condensers 4% and 15, and the transmitter feed coil 10.

CD illustrates a well known dial device provided for the use of the attendant in establishing connections. The contact of this dial is closed upon moving the finger disk olf normal, and remains closed during the time the disk revolves back to normal position, while the contacts Y6 are opened and closed in rapid succession during the back-tonormal movement, to transmit the desired number of impulses for operating the automatic switches used in the extension of a call.

Throughout the drawing there are shown a number of battery and ground connections. This has been done for convenience only, and isin accordance with common practice of schematic representation. In actual use, there is of course only one battery, preferably with the plus pole grounded.

Having given a. general account of the invention and of the drawing, the detailed description will not be proceeded with. For this purpose, it will be assumed first that the branch exchange station A desires a connection with the branch exchange station E, both stations terminating at an attendants switch board, and that the attendant establishes this connection by means of the cord circuit illustrated.

When the subscriber A. removes his receiver, in order to extend a call, he closes the line loop, thereby energizing the line relay 1. This relay closes its armature E2 and lights the calling lamp L. The operator, noticing the lighted lamp, inserts the plug l? into the line jack J. The following circuit is closed thereby: from ground, upper winding of the line relay 79, contacts 22 of NT, contact spring 12 of the ringingkey BK, talking strand 17, tip conductor of plug P and jack J, line conductor R, line loop, and back over the line conductor T, ring conductor of jack J and plug P, talking strand 18, spring 13 of the ringing key and contact 25 of the key NT, lower winding of the line relay 7 9 to battery. Relay 79 operates its armature 80, thereby closing the circuit for relay from battery, winding of relay 85, armature 92 and its back contact, front contact and armature 80, sleeve conductor 19, sleeve of plug P and sleeve of jack J to ground. Relay 85 open ates and prepares at its armature 86 the relay 81 and the supervisory lamp 16. At its armature 87 the relay 85 locks itself to ground on the sleeve conductor 19, independ ent of armature 80 of relay 79. However, the locking circuit for relay 85 has at the present time no significance.

The attendant operates her listening and dial key Ll). This action on the part of the attendant results in the following circuitsz IOU relay 98 operates from battery, winding of relay 98, conductor 47, contacts of the listening key, conductor 46, and back contact and armature 97 to ground, and closes its armatures 99 and 100, thereby connecting the operators head-set O to the talking strands of the cord circuit, by way of the contacts 67 and 70 of the listening key. At contact 66 of the listening key, the dialing circuit is prepared; and at contact 71 the locking circuit for relay 85, which has previously been mentioned, is opened.

The attendants telephone set is now connected; the conversational circuitextends as follows: from the upper terminal of the secondary winding'of the induction coil 42 by way of front contact and armature 99, conductor50, closed contacts 67 of the dialing key, conductor 36, conductor 30, contact 20 of the through-dialing-key, conductor 32, back contact and armature 82, condenser 28, contact 22 of the through-dialing-key, contact 12 of the ringing key, talking strand l7, tip conductors of plug P and jack J,line conductor R, substation, line conductor T, ring conductors of jack J and plug P, talking strand 13, contact 13 ofthe ringing key, contact 25 of the through-dial-key, condenser 29, armature 84 and its back contact, conductor 33', con tact 27 of the through-dialing key, conductor 31, conductor 37, contact 70 of the listening key, conductor 60, armature 100 and its front contact, condenser 45, receiver 43, to the lower terminal of the'secondary winding of the induction coil 42. The operator receives the information from the calling party that a connection is desired to the substation B. The operator inserts the calling plug P of the cord circuit into the ack of the called line. The line relay 3 of the called line is thereby disconnected, and ground is connected from the sleeve conductor of ack J over the sleeve of plug P, conductor 56, winding of the sleeve relay 39, to battery. The sleeve relay operates in this circuit and opens at its armature 92 the circuit for relay 85; at its armature 91, ground is connected for lighting the supervisory lamp 39; and at the armatures and 93, the impedance 88 is disconnected from the talking conductorsv of the cord, and the back bridge relay 94 is connected in bridge of these conductors. i

The operator aetuates now the ringing key BK thereby project-ing ringing current out to the called line, froin ground, closed contacts 68 of the ringing key RK, talking strand 54, tip conductors of plug P and jack J, line conductorR, bells of the called substation, line conductor T ring conductors of jack J and plug P,'talking strand 55, closed contacts 74 of the ringing key RK, and generator G. l Vhen the c'alled party removes the receiver in answering the call, the back bridge relay will operate from ground, up-

per'winding of relay 94, front contact and armature 90 of the sleeve relay 89, conductor 34, conductor 32, contact EEO-of the throughdial-key, conductors 30, 36, 51, normally closed contacts operated by armature 105, conductor 53, contact 69 of the ringing key, conduct-or 54, tip conductor of plug P and jack J, over the previously traced line circuit, and back over the ring conductor of jack J and the plug P, conductor 55, contacts 73 of the'ringing key, conductor 57, normally closed I contacts operated by arn'iature 107, conductors 59, 37, 31, contact 2701 the through-dial-- key, conductors 33 and 35, armature 93 andits front contact, through the lower winding of the back bridge relay 94 to battery. The backbridge relay operates its armature 95 and extinguishes thereby the answering su pervisory lamp 39.

The subscribers are now connected in atalking circuit and receive their transmitter feed over the line relay 79 and over the back. bridge relay 94, respectively, both of these relays being connected to the talking conductors of the cord, but separated in the usual manner by the condensers 28 and 29. Itha's been mentioned previously that'the operatorby operating her listening key LD has also prepared the dial. This function of the listening key has of course no significance in the present case, since the called party is a branch exchange subscriber. The cord circuit servesmerely as a link for establishing the con nection.

Should one of the parties desire the presence of the operator he may recall the operator by simply jiggling his switch hook. If the calling party does so, the relay 79 will be deenergized intermittently, and at each time this relay deenergizes a circuit will be closed for the answering supervisory lamp 16, from ground on the sleeve conductor 19, armature 80 and its back contact, armature 78 and its back contact, and lamp 16 to battery. In case the called party operates the switch hook,'the back bridge relay 94 will deenergize and, at its armature 95, close a circuit for the calling supervisory lamp 39 from ground, front contact and armature 91 ofthe sleeve relay 89, back contact and armature 95, and calling supervisory lamp 39 to battery. Thus, the operator will receive flash signals from the subscribers and again operate the listening key LD to answer the re-' quest. 9 I 1 At the termination of a call, both parties hang up their receivers. The relays 79 and 94 deenergize, and thereby light the lamps 16 and 39 over circuits which have been traced already. The lighted lamps serve as a disconnect supervision for the operator. She removes the plugs-P and P from the line jacks J and J. All apparatus is then restored to normal position and the cord circuit is ready for the next call.

It shall be assumed now that the subscriber at substation -A desires a connection with a main exchange station over the trunk line C, and it shall further be assumed that the operator at the branch exchange serves as a medium for dialing the wanted partys number. Up to the point where the operator gets her information from the substation A, every operation is the same as discussed above. In-

. stead of inserting the plug P into a line jack J, the attendant operator inserts this plug into the jack J 2 of the trunk line C. In doing so, the contact 11 of the jack J is closed, and relay 8 energizes. This relay operates its armature 9 and disconnects thereby the ringing relay 5 from the trunk conductors R and T In the case Where the operator inserted the plug P into the line jack J the sleeve relay 89 energized from ground on the sleeve conductor of the jack J. In the present case, no energization of the sleeve relay 89 takes place, since the sleeve conductor of the trunk jack J 2 is not connected to ground. The relay 85 remains therefor operated. This is of significance in connection with the release of the switches in the main exchange and shall be described later. Due to the sleeve relay 89 not being energized in this connection, the impedance 88 remains in bridge of the talking conductors of the cord circuit. This bridge is used for holding the switches in the mainexchange, and may be traced, from the upper terminal of the impedance 88, back contact and armature 90 of the sleeve relay 89, conductors 34, 32, contacts 20 of the through-dial-key, conductors 30, 36, 51, normally closed contacts operated 'by armature 105, conductor 53, contacts 69 of the ringing key, conductor 54, tip conductors of plug P and ack J contact 10 of jack J trunk conductor R to the main exchange, and back, over the trunk conductor T ring conductor of the jack and plug, conductor 55, contacts 73 of the ringing key, conductor 57, normally closed contacts operated by armature 107, conductors 59, 37, 31, contacts 27 of the through-dial-key, conductors 33 and 35, armature 93 and its back contact, back contact and armature 83, to the lower terminal of impedance 88. The calling subscriber is connected as usual to ground and battery over the windings of the line relay 79; and the operators circuit is connected, as in the former case, over the armatures 99 and 100 of the relay 98, due to the dial key being in operated position. There is also an alternating current bridge in this circuit which includes the relay 96 and the condenser 38. This bridge will be of significance in connection with the recall feature mentioned elsewhere, which shall be described later.

The operator moves the dial GD ofl' normal in accordance with the first digit of the called subscribers number. The ofienormal contact 75, of the dial CD is closed thereby, oper ating the relay 101. This relay operates its armature 102, connecting ground from the off-normal contacts 75 of the dial by Way of contacts 66 of the listening key and conductor 49, to relay 104 and battery. Relay 104 operates and connects thereby the impulse contacts 76 of the dial CD, across the talking conductors of the trunk circuit, disconnecting the branch exchange end of the cord. In returning to normal, the dial interrupts the impulse springs 7 6 in rapid succession, thereby interrupting the trunk circuit and operating a switch in the main exchange. This action will be repeated on the part of the operator for each digit of the called subscribers tele' phone number.

When the relay 101 operates it also closes its armature 103, thereby short circuiting the receiver 43 of the operators telephone set. It will be obvious that the short circuiting of the receiver prevents disturbing clicks in the operators head phone.

lVhile the operator is dialing, the Waiting subscriber is connected to battery and ground over the windings'of the relay 79. If the waiting party decides to abandon the call during the dialing period, relay 79 Will deenergize in response to the subscriber replacing his receiver, and close its armature 80,

thereby completing a circuit for the answermg supervisory lamp 16, from ground on the sleeve conductor 19. Relay 81 energizes in this case in parallel to the answering supervisory lamp 16 by way of armature 86 of relay 85, which, it will be remembered, is in operated position. Relay 81, operates its armatures 82 and 84, thereby cutting the cord circuit at the condensers 28 and 29. Armature 83, being also opened by the energization of relay 81, serves to disconnect the impedance 88 from across the talking conductors of the cord.

Now, scrutinizing the function of the dial a little closer, it will be seen that the relay 101 is a slow acting relay and does not deenergize during the dialing, while relay 104 which completes the impulse circuit over the armatures 105 and 107 is an ordinary quick acting relay and deenergizes during the intervals between the digits. Assuming that the subscriber has not hung up his receiver, the relay 104 in deenergizing will connect the impedance 88 in bridge of the talking conductors of the trunk line over a circuit traced before. The switches in the main exchange will therefore be held energized, or rather to say, be

the calling subscriber has abandoned the call. She will not continue to dial the remaining digits oi the called telephone number, but will simply withdraw the plugs P and P from the respective jacks, and thereby restore all apparatus normal position.

I1 the waiting party does not abandon the call, the operator continues to dial the remain ing digits of the wanted partys number and, after finishing the dial operation, she will withdraw by restoring her dial-anddistening key LD.

When the calling party replaces his receiver at the termination of the call, relay 79 deenergizes, and relay 81 operates as before in parallel with the answering supervisory lamp 16. The lighted lamp indicates to the 0perator that the call has terminated, while the operation of relay 81 serves, as in the previous case, to open the trunk conductors by removing the impedance 88, and thereby restoring the switches in the automatic main exchan e in the same manner as is usual in calls between two automatic stations.

It shall be assumed next that the operator delays withdrawing the plugs P and P from the respective jacks. As far as the main exchange is concerned, the trunk C is to all intents and purposes idle and can be used for calls from the main exchange to the branch exchange, and it shall be assumed that the trunk C is seizedirom the main exchange and that ringing current is transmitted over he trunk conductors R and T The ringing current applied to the trunk line operates the ringing relay 96, which is bridged across the talking conductors of the cord circuit. This circuit can readily be traced over the conductors 36, 51, normal contacts of armature 105, conductor 53, contacts 69, conductor 54, tip conductors of plug P and jack J trunk conductor R to the main exchange, and l'lttCrZ over trunk conductor T contacts 10, ring conductor of the jaclrand plug, conductor 55, contacts 73, conductor 5?, normal con tacts of armature 107, conductors 59 and 37, condenser 38 and relay 96. Relay 96 operates in response to ringingcurrent over the trunk line and closes the armature 97. The supervisory lamp 39 will therefore light during the ringing periods. According to what ringing method is being used in the main exchange, that is to say, in accordance with where the call came from, whether ringing current is applied automatically or manually by depressing a ringing key in the main ex change, the supervisory lamp will either flash regularly and rapidly, or will be irregular and of longer duration.

The attendant operator, observing the flashing of lamp 39, operates her listening key I'D, to connect her telephone set to the cord. It will be remembered that the connection of the telephone set is dependent on relay 98. This relay, heing connected at one terminal the flashing signal 96 is in normal or deenergized position. In

other words, the energization of relay 98, and consequent connection of the operators telephone set to the cord, is only possible during a silent period, when relay 96 is deenergized. Therefore, ringing current cannot enter the operators telephone set. The operator will then remove the plug P from the line jack J, and ascertain the wishes of the main exchange.

It will be seen from the description of the functions of the cord circuit, while ringing current was applied to the trunk line, and before the operator in the branch exchange has taken down the connection, as was as sumed in the preceding paragraph, that the trunk conductors terminate in the re-ring relay 96, while the answering end of the cord, which is still connected to the party in the branch exchange, is disconnected at armatures 82 and 8% of relay 81. The impedance 88 is removed from the talking conductors. This of course prevents ringing current from annoying the substation by ringing the bell thereat.

In case the connection described last, extending from a branch exchange subscriber A to the main exchange over the trunk line C had been one to a manual exchange, the functions of the cord circuit would have been substantially the same. Dialing of course would have been unnecessary. The operator would have simply inserted the plug P into the jack J The operator at the manual ex change would have beeninformed of the subscribers Wishes, either by the attendant operator in the branch exchange, or by the branch exchange subscriber himself, in an. obvious manner. The impedance 88 would have been connected as usual across the talking conductor from the trunk circuit, providing supervision for the main exchange manual operator. In this case if the attendant operator at the branch exchange would have delayed taking down the connection, the recall signal may also be utilized. The difference in operation resides merely in the fact that the trunk line would not be selected by a switch in the main exchange but by a manual operator. Ringing current also would be'applied manually from the main exchange, operating relay 96, and signaling the branch-exchange attendant as before. In this case also, the ringing current applied-tor recalling the branch exchange attendant, could not enter the private branch exchange 'subscribers sta- 7 The extension next to be described, shall be one from the main exchange, by way oi the trunk line C, to a subscriber in the branch exchange. The trunk line is either seized in the main exchange by means of a well known rotary connector, ii the main exchange is automatic, or the trunk line is taken into use from a manual excl'iange, in the usual way, by an operator. Ringing current is projected over the trunk conductors R and T operating the ringing relay-5. When this relay energizes, it closes its armature 6 and lights tl e trunk lamp L The attendant operator in the branch exchange, observing the lighted trunk lamp L inserts the plug P into the ack J This action closes spring contacts 11 in the jack J thereby completing an obvious circuit for relay 8, which removes the ringing relay 5 by opening its armature 9. The line lamp L extinguishes. The impedance 88 is now again in bridge of the trunk conductors furnishing an answering signal to an operator in the main exchange, if the call should have been originated in a manual exchange, and cutting oti' the ringing current, if the call should have been initiated in an automatic exchange.

The attendant in the branch exchange operates her listening and dial key LB, connecting her telephone set to the trunk circuit in the usual manner. She receives then the request 01 the waiting main exchange subscriber, and connects the Wanted branch exchange station by inserting the plug lP into a line jack, such as J or J, of the desired station. In response to the insertion of the plug P into the line jack of the desired party, the answering supervisory lamp 16 lights. The attendant then operates her ringing key RK and projects ringing current out on the line to the branch exchange subscriber. When the called subscriber removes his receiver from the switch-hook, in answering the call, (the ringing key is at normal during a silent period) the relay 79 will energize, xt-inuishing the answerin su ervisor lam a 16 and energizing relay 85 as before. Reiay 85 closes its armature 87 to lock itself energized to the sleeve conductor 19, and prepares the relay 81 by closing its armature 86. The im pedance 88 is again connected across the talking conductors, as the case in previously described extensions. The calling main exchange subscriber and the called branch exchange station are now connected in an obvious talking circuit; the supervisory lamps 16 and 39 are extinguished.

Upon the subscribers hanging up their re-' ceivers at the termination of a call, the branch exchange attendant receives disconnect supervision by having the answering supervisory lamp 16 lighted over the back contact 80 of the now de'energized relay 79. Parallel to lamp 16 the relay 81 will energize as pre-' at its armatures 82 and 8 1, while removing the impedance 88 from across the trunk conductors, at its armature 83. It the call was one from a manual exchange, the removal of the impedance 88 will furnish disconnect supervision for the manual operator of the main exchange; it, on the other hand the call had been one originated in an automatic main exchange, the removal of the impedance 88 will effect the release of the automatic switches. This function of the cord circuit has already been described.

As in a case previously explained, the attendant at the branch exchange may be recalled it' the trunk C is again taken into use and in case the operator has relayed taking down the connection. The operations involved in recalling the attendant have already been explained and shall not be repeated a this point. r

As is obvious from the above explanation, tie different kinds of services described so far, are possible with the cord circuit shown and without the operation of any circuit changing key. A number of services shall be explained next, which require the operation of the night service, toll, and through-dialingkey NT. For this purpose it shall be assumed that the branch exchange subscriber A desires a connection to an automatic main exchange party by way of the trunk line, and itshall further be assumed that the branch exchange subscriber is to dial the number of the wanted party in the automatic main exchange.

In this case, the branch exchange attendant operates her listening key in the usual manner, after she has inserted the plug P into the calling line jack, and receives the wishes of the calling subscriber. She then operates the througl1-dialing-key NT and restores her listening key LD. By this action, the calling branch exchange subscriber is connected through to the main exchange (it being assumed of course that the operator has inserted the calling plug P into the trunk jack J the through circuit being traceable, from the .calling branch exchange station over the line conductor T, ring conductor of the jack J and of the plug P, conductor 18, contacts 13.

ringing key RK,. conductor 17, tip conductors i of plug P an'd jack J, and line conductor R back to the calling substation.

The main exchange being assumed to be an automatic exchange, the trunk C terminates in an automatic switch. The calling branch exchange substation'is therefore connected to this automatic switch in the main exchange in a loop circuit, comprising the series relay 77. Relay 79, is, in this case, not operated because it is disconnected from the cord circuit at contacts 22 and 25 of the through-dialing-key NT. Accordingly, ground is connected from the sleeve conductor 19, by way of armature and its back contact, to the armature 78 of the series relay 77. Relay 77 is energized at present over the subscribers loop circuit to the automatic switch at the main exchange. The subscriber dials now the wanted telephone number in the usual manner by interrupting the line loop.

The relay 77 may or may not operate in response to the line interruption, according to the total line and trunk" resistance. If this relay operates, the supervisory lamp 16 will be flashed. The attendant at the branch exchange will thereby receive asignal that the substation is dialing. If this relay does not respond to the impulses transmitted at the substation, the operator will not receive any signal. The'relay77 can, of course, be adjusted to either operation. Since the operator, however does not enter this call, or rather to say, does not efi'ect itsextension, the operation of relay 77 during dialing is quite immaterial.

When the calling branch exchange subscriber replaces his receiver at the termination of the call, the series relay 7 7 deenergizes and lights the supervisory lamp 16. 'The branch exchangeattendant, observing that lamp 16 lights steadily, knows that she has to disconnect the plugs P and P from the respective jacks. The main exchange switches will release when the branch exchange subscriber replaces his receiver, due to the loop circuit being opened.

In case the operator delays taking down the connection, and the trunk is again selected from the main exchange, ringing current applied to the trunk conductors Pt and T will operate the ringing relay 96 in the cord circuit, in the usual manner, and flash the lamp 39. In this case, however, since the branch exchange subscriber is supposed tohe still connected to the cord circuit, he will also receive the recall signal. I

For toll connections, the procedure is sub stantially the same as that described above, with the difference that the branch exchange subscriber may or may not have to dial, according whether the trunk circuit C terminates at a manual toll position or in an automatic switch which has access to a toil operator. Since the branch exchange subscriber is connected in a loop circuit to the main exchange (the through-dialingkey being thrown) it is obvious that the toll operator will receive supervision from the branch exchangesubscriber. Disconnect supervision for the branch exchange attendant is accomplished in the same manner as described previously, that is, the supervisory lamp 16 will be lighted steadily when the branch exchange subscriber hangs up his receiver.

In night service, the plug P 01 the cord will be connected to a certain subscriber of the branch exchange, and the plug P will be inserted into jack J of the trunk circuit C. It may be mentioned at this point that it is usual practice in branch exchanges, to disconnect battery during the night. Now, if itis assumed that the branch exchange subscriber, thus connected to a trunk, is about to make a call to the main exchange, he re moves his receiver and is immediately connected in a loop circuit including the series relay 77, which circuit has been traced and explained in connection with previousextensions. He therefore receives transmission feed from the main exchange, and may dial the desired main exchange subscriber as usual. v

If, on the other hand, the main exchange subscriber desires to call the branch exchange party during the night, ringing current will be transmittedover the trunk conductors R and T operating the relay 96 in the cord circuit. If it is assumed that the battery is disconnected from the branch exchange, the operation of relay 96 will of course not have any effect. If battery is still connected, the signal lamp 39 will light. As no operator is attending'to the branch exchange switch board, the operation of the signal lamp 39 is of no significance. The branch exchange subscriber, being connected through, however, will also receive a ringing signal, and will answer the call.

Having described the invention in detail, it will be seen that many advantages are presented which are not foundin prior disclosures. The invention has been described in connection with a specific structure, but it will, of course, be understood that a variety of Ways forcarrying out the invention differently without departing from its spirit will suggest" themselves readily. Accordingly, the executioner the invention is not intended to be limited to the precise structure shown. What is considered new will be pointed out in the appended claims.

lVhat is claimed is:

1. In a telephone system, a calling line, a called line accessible over a trunk line and automatic switches, a cord circuit, means for connecting said cord circuit to said calling line and to saidtrunk line, an impulse device, an operators telephone set including a receiver, means for establishing a talking circuitbetween said calling line and said telephone set, means for actuating said impulse device to transmit impulses over said trunk line for operating said automatic switches to extend a connection from said calling to said called line, a single relay means operable upon and during the actuation of said impulse device for connecting said impulse device to said trunk line, for interrupting the continuity of said cord circuit, and for shortcircuiting said receiver, and means controlled by said calling line for signalling the opera tor during the transmission of impulses.

2. In a telephone system, a calling line, a-

impulse device for connecting the same to said trunk line to transmit impulses thereover for operating said automatic switches to extend a connection from said calling to said called line, said relay means also operable for interrupting the continuity of said cord circuit and for short-circuiting said receiver to prevent disturbing clicks from entering the calling line and said operators tel ephone set, and means, controlled by said calling line for signalling the operator while impulses are being transmitted.

3. In combination, a calling telephone station connected over a link circuit to a trunk line, an operators set including a telephone receiver, an impulse sending device for transmitting series of impulses, means for actuating said sending device, and single electromagnetic means responsive to the actuation of said sending device arranged to short circuit said receiver, to connect said sending device to said trunk line and to break the continuity of said link circuit, said last means completing the continuity of said link circuit at the termination of the transmission of each series of impulses.

4:. In combination, a private branch exchange telephone station connected over a cord circuit With a trunk line terminating,

change telephone station connected over a cord circuit with a trunk line terminating in a main exchange, means in sa1d main exchange for projlectmgringing current over said trunk line, a relay in said cord circuit responsive to said ringing current, a supervisory signal associated with said cord circuit and operable by said relay, means in said cord circuit arranged to prevent the propagation of ringing current to said branch exchange station, an operators telephone set,

means for connecting said telephone set with said cord circuit, and automatic means arranged to prevent the connection of said telephone set to said cord circuit during a ringing period.

6. In a telephone system, a calling line, :1 called line accessible over a trunk line and automatic switches, a cord circuit having a first section adapted to be connected to said calling line, and a second section conductively separated from said first section and adapted to be connected to said trunk line, an impedance bridged across said second section, an impulse device for transmitting trains of impulses over said trunk line to operate said automatic switches, a single relay means operable upon actuation of said device and during the transmission of an impulse train, for connect-ing said device to said trunk line and for disconnecting said impedance while an impulse train is being transmitted and re connecting said impedance at the termination of an impulse train, and means controlled by said calling line for permanently disconnect-ing said impedance to effect the release of said automatic switches upon termination of the transmission of an impulse train.

7. In a telephone system, a calling line, a called line accessible over a trunk line and automatic switches, a cord circuit having a first section adapted to be connected to said calling line, and a second section conductively separated from said first section and adapted to be connected to said trunk line, an impedance bridged across said second section, an impulse device for transmitting trains of impulses over said trunk line to operate said automatic switches, a single relay means operable upon actuation of said device and during the transmission of an impulse train, for connecting said device to said trunk line and for disconnecting said impedance while an impulse train is being transmitted and re connecting said impedance at the termination of an impulse train, a visual signal, and means in said first section controlled by said calling line for permanently disconnecting said impedance to effect release of said automatic switches upon termination of the transmission of an impulse train, and also effective for actuating said signal.

8. In a telephone system, a calling line, a called line accessible over a trunk line and automatic switches, a cord circuit having a first section adapted to be connected to said calling line, and a second section conductively separated from said first section and adapted to beconnectedto said trunk line,

an impedance bridged across said second section, an impulse device for transmitting trains of impulses over said trunk line to op erate said automatic switches, a single relay means operable upon actuation of said device and during the transmission of an impulse train, for connecting said device to said trunk line and for disconnecting said impedance while an impulse train is being transmitted and reconnecting said impedance at the termination of an impulse train, a visual signal, a relay, means in said first section controlled by said calling line for actuating said relay and said signal, and means operated by said relay for permanently disconnecting said impedance to eilect the release of said automatic switches upon termination of the transmission of an impulse train. I

9. In a telephone system, a calling line, a called line accessible over a trunk line and automatic switches, a cord circuit having a first section'adapted to be connected to said calling line, and having a second section conductively separated from but inductively connected to said first section and adapted to be connected to said trunk line,

an alternating current bridge and a direct current bridge connected across said second section in parallel, an impulse device, a single relay means operable upon and during the actuation of said device for connecting said device to said trunk line to, transmit a train of impulses thereover and for disconnecting said bridges during said impulse transmission but reconnecting said bridges upon the termination of transmission of an impulse train, and means in said first section controlled by said calling line for disconnecting said direct current bridge to effect the release of said trunk line upon termination of an impulse train while leaving said alternating current bridge connected across said second section.

10. In a telephone system, a calling line, a called line accessible over a trunk line and automatic switches, a cord circuit having a first section adapted to be connected to said calling line, and having a second section conductively separated from but inductively connected to said first section and adapted to be connected to said trunk line, an alternating current bridge and a direct current bridge connected across said second section in parallel, an impulse device, a single relay means operable upon and during the actuation of said device for connecting said device to said trunk line to transmit a train of impulses thereover and for disconnecting said bridges during said impulse transmission but reconnecting said bridges upon the termination of transmission of an impulse train, a relay, means in said first section controlled by said calling line for actuating said relay, means operated by said relay for disconnecting said direct current bridge to effeet the release of said trunk line upon termination of the transmission of an impulse train, and means actuated by said relay for interrupting the inductive continuity of said cord circuit sections. 7

11. In a telephone system, a calling line a called line accessible over a trunk line and automatic switches, a cord circuit having a first ection adapted to be connected to said calling line, and having a second section conductively separated from but inductively connectedto said first section'and adapted to be connected to said trunk line, an alternating current bridge and a direct current bridge connected across said second section in parallelyan impulse device, a single relay means operable upon and during the actuation of said device for connecting said deviceto said trunk line to transmit a train of impulses thereover and for disconnecting said bridges during said impulse transmission but reconnecting said bridges upon the termination of transmission of an impulse train, a relay and a signal, means in said first section controlled by said calling line for actuating said relay and said signal, and means operated by said relay for disconnecting said direct current bridge to effect the release of said trunk line upon termination of the transmission of an impulse train, and for interrupting the inductive continuity of said cord circuit sections, said alternating current bridge remaining connected across said second section of said cord circuit in order to provide a means for receiving signals transmitted over said trunk line.

12. In a telephone system, a calling line, a called line accessible over a trunk line and automatic switches, a cord circuit having a first section adapted to be connected to said calling line, and having a second section conductively separated from but inductively con nected to said first section and adapted to be connected to said trunk line, an alternating current bridge, a relay, a signal, means in said first section controlled by said calling line for actuating said relay and said signal, means operated by said relay for disconnecting said direct current bridge to efiect the release of said trunk line while leaving said alternating current bridge connected across said second section to provide a means for receiving signalling current transmitted over said trunk line, and other means actuated by said relay for interrupting the conductive continuity of said cord sections to prevent said signalling current from effecting said calling line.

In witness whereof, I hereunto subscribe my name this 24th day of August, A. D.,

CHRISTIAN J LARSEN. 

